Microbiome-Based Therapies in Ulcerative Colitis: Mechanisms, Clinical Evidence, and a Precision-Medicine Framework.

Microbiome-based therapies are reshaping the therapeutic landscape for ulcerative colitis (UC), offering new avenues for disease management beyond conventional immunomodulatory and biologic treatments. UC remains a chronic, relapsing condition with significant unmet clinical needs, as many patients fail to achieve sustained remission or experience adverse effects with current therapies. The gut microbiome has emerged as a central contributor to UC pathogenesis, influencing epithelial barrier integrity, immune homeostasis, and metabolic signaling. Interventions such as fecal microbiota transplantation (FMT) and defined microbial consortia have demonstrated proof-of-concept efficacy in early-phase clinical trials, each leveraging distinct mechanistic strategies. FMT, as a broad ecological intervention, restores microbial diversity and functional redundancy, potentially addressing multiple pathogenic mechanisms simultaneously. In contrast, defined consortia enable precise targeting of specific metabolic and immunological pathways, including short-chain fatty acid production, bile-acid remodeling, epithelial barrier reinforcement, immune modulation, and succinate degradation. Recent clinical evidence suggests that consortia with broader mechanistic coverage may achieve more consistent biological activity than narrowly focused designs. This review synthesizes mechanistic and clinical insights across broad and defined microbial consortia, integrates evidence from randomized controlled trials and early-phase LBP studies, and outlines a precision-medicine framework to guide therapy selection. We highlight the importance of aligning therapeutic mechanisms with patient-specific microbial, metabolic, and immune profiles, and discuss future directions including biomarker-guided stratification, hybrid consortia, and adaptive trial designs. Advancing both broad and defined approaches, while incorporating ecological principles, mechanistic understanding, and patient stratification, will be essential to realizing the full therapeutic potential of microbiome-based therapies in UC.